Medical devices to be inserted into a living body, such as catheters, guide wires and the like, can exhibit excellent lubricity in order that damage of tissues such as blood vessels is reduced and handleability by an operator is improved. Hence, there have been developed and put into practice methods of coating a base material surface with a hydrophilic polymer having lubricity. In such medical devices, elution and peeling-off of the hydrophilic polymer from the base material surface present a problem in maintaining safety and handleability.
In order to avoid such a problem, Japanese Patent Laid-Open No. Hei 8-33704 discloses a medical device wherein a water-soluble or water-swelling polymer is dissolved in a solvent capable of swelling a base material of the medical device to prepare a polymer solution, and the base material of the medical device is swollen by immersion in the polymer solution, followed by crosslinking or converting the polymer into a higher molecular weight product on the base material surface, thereby forming a surface lubricating layer on the base material surface.
In the method described in the above-indicated Japanese Patent Laid-Open No. Hei 8-33704, the surface lubricating layer can be strongly fixed on the base material to some extent. Especially where the base material is made of a polymer material and the base material per se is swollen with a hydrophilic polymer solution, very strong fixing is enabled by the formation of an interpenetrating network structure of the base material polymer and the hydrophilic polymer formed as the surface lubricating layer. On the other hand, where the base material is made of a metal material, the hydrophilic polymer serving as the surface lubricating layer is fixed on the base material only by the insolubilizing effect, involving a higher risk that the surface lubricating layer is peeled off when compared with the polymer base material. Thus, there is a need for a coating method wherein a hydrophilic polymer can be fixed more strongly on a metal base surface.
A known method of fixing a hydrophilic polymer on a metal base involves carrying out a primer treatment. For instance, Japanese Patent Laid-Open No. 2007-267757 discloses a method wherein a base metal is pre-treated with a primer including, as an essential component, an adhesive organic compound having, in the molecule, at least one functional group capable of adsorption on a metal and at least one reactive functional group and a film of a hydrophilic polymer is formed thereon to improve adhesion between the surface lubricating layer and the metal base.
However, the method set out in the above-mentioned Japanese Patent Laid-Open No. 2007-267757 has had a problem in that the surface lubricating layer is not sufficiently strongly fixed on the metal base.